Birds

UXL Encyclopedia of Science
COPYRIGHT 2002 The Gale Group, Inc.

Birds

Birds are warm-blooded vertebrate (having a backbone) animals whose bodies are covered with feathers and whose forelimbs are modified into wings. Most can fly. Birds are in the class Aves, which contains over 9,500 species divided among 31 living orders. One order, the Passeriformes or perching birds, accounts for more than one-half of all living species of birds.

Most scientists believe that birds evolved from saurischian dinosaurs about 145 million years ago. The first truly birdlike animal, they point out, was Archaeopteryx lithographica, which lived during the Jurassic period. Fossils from this animal were found in Germany in the nineteenth century. This 3-foot (1-meter) long animal is considered to be an evolutionary link between the birds and the dinosaurs. It had teeth and other dinosaurian characteristics, but it also had a feathered body and could fly.

A fossil discovery by scientists in 2000, however, threw into doubt the theory of birds' evolution. The fossils in question were excavated in 1969 in Kyrgyzstan, a former Soviet republic, but were not correctly identified until some thirty years later. The animal, Longisquama insignis, lived in Central Asia 220 million years ago, not long after the time of the first dinosaurs. From impressions left in stone, it had four legs and what appeared to be feathers on its body. Scientists who analyzed the fossils said the animal had a wishbone virtually identical to Archaeopteryx and similar to modern birds. It was a small reptile that probably glided among the trees 75 million years before the earliest known bird. Some scientists believe this challenges the widely held theory that birds evolved from dinosaurs.

Modern characteristics

The bodies of birds are covered with specialized structures known as feathers that grow out of the skin. No other animal has them. Feathers act as a barrier against water and heat loss, are light but very strong, and provide a smooth, flat surface for pushing against the air during flight. The feathers of most species have color, often bright and beautifully patterned, that serves as camouflage and is used in courtship displays by males.

The modified forelimbs, or wings, of birds are used for flying or gliding. The hind limbs are used for walking, perching, or swimming. Swimming birds typically have webbed feet that aid them in moving through water. The bones of the flying birds are structured for flight. They are very light and have many hollow regions. The wing bones are connected by strong muscles to the keeled, or ridged, breastbone, and the pelvic bones are fused so that they are rigid in flight.

The jaws of birds are modified into a horny beak, or bill, that has no teeth and that is shaped according to the eating habits of each species. Like mammals, birds have a four-chambered heart that pumps blood to the lungs to receive oxygen and then to the body tissues to distribute that oxygen. Fertilization occurs internally, and the female lays hard-shelled eggs—usually in some type of nest—that have a distinct yolk. One or sometimes both parents sit on the eggs until they hatch, and the young of almost all species are cared for by both parents.

Words to Know

Barb: The branches of a feather that grow out of the quill and are held together by barbules in flying birds.

Barbules: Hooks that hold the barbs of a feather together in flying birds.

Bill: The jaws of a bird and their horny covering.

Feathers: Light outgrowths of the skin of birds that cover and protect the body, provide coloration, and aid in flight.

Keel: The ridge on the breastbone of a flying bird to which the flying muscles are attached.

Quill: The hollow central shaft of a feather from which the barbs grow.

The keen eyesight and sensitive hearing of birds aid them in locating food. This is important because their high level of activity requires that they eat often. Birds are also very vocal, using various calls to warn of danger, defend their territory, and communicate with others of their species. Songbirds are any birds that sing musically. Usually, only the male of the species sings. The frequency and intensity of their song is greatest during the breeding season, when the male is establishing a territory and trying to attract a mate.

Birds are found the world over in many different habitats. They range in size from the smallest hummingbird, at less than 2 inches (6 centimeters), to the largest ostrich, which may reach a height of 8 feet (2.4 meters) and weigh as much as 400 pounds (182 kilograms). Many species of birds migrate hundreds or even thousands of miles south every autumn to feed in warmer climates, returning north in the spring.

Flightless birds

Flightless birds lack the keel (high ridge) on the breastbone to which the flight muscles of flying birds are attached. Instead, the breastbone is shaped like a turtle's shell. It has also been described as a raft, giving this group of birds its name, Ratitae (from the Latin ratis, meaning "raft"). Ratites have heavy, solid bones and include the largest living birds, such as the ostriches of Africa and the emus of Australia. Kiwis, another type of flightless bird, live in New Zealand and are about the size

of chickens. The penguins of Antarctica are also flightless but are not regarded as ratites. Their powerful flight muscles are used for swimming instead of flying.

Ratites are the oldest living birds and are descended from flying birds who lost the ability to fly. The feathers of ratites differ in structure from those of flying birds. They lack barbules—hooked structures that fasten the barbs of the quill together, providing an air-resistant surface during flight. Instead, the strands that grow from the quill separate softly, allowing air through. This softness makes the feathers of many ratites particularly desirable. Ostrich plumes, for example, have long been used as decoration on helmets and hats.

Human impact on birds

Humans have destroyed birds, both intentionally and unintentionally. Two hundred years ago, birds were considered such an inexhaustible resource that wholesale slaughter of then hardly raised a concern. The greatest impact humans have had on birds has been brought about through human expansion (farms, cities, roads, buildings) into their natural habitats. A by-product of industrial development has been widespread environmental pollution. Pesticides, used on farms to rid fields of insects, have accumulated in many places frequented by birds and have been subsequently ingested by them. Oil spills have also taken their toll on bird populations. It is not surprising, then, that many species have disappeared as a result of human activities and encroachment on the natural environment. According to one scientific estimate, 85 species of birds, representing 27 families, have become extinct since 1600.

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Bird

Biology
COPYRIGHT 2002 The Gale Group Inc.

Bird

Birds are warm-blooded vertebrates with feathers. They are thought to have evolved over 150 million years ago from a Mesozoic reptilian ancestor. Indeed, they share many characteristics with reptiles, including nucleated red blood cells, females as the heterogametic sex (having two different sex chromosomes ), numerous skeletal features, and similar eggs. However, birds have evolved many unique characteristics.

Characteristics of Birds

The most remarkable of the bird's characteristics is the feather. Feathers are the diagnostic trait of birds. No other living animal has feathers. The contours and strength of feathers make bird flight possible. At the same time they are lightweight and provide excellent insulation and physical protection to the bird's body. Feather coloration provides both concealment and a means of communicating with rivals and mates. Feathers are energetically inexpensive to produce, and a bird can grow at least a partial new feather coat each year.

Birds are highly skilled, powerful flyers. Flying, however, is an energetically costly activity, and there is hardly any aspect of avian anatomy that has not been influenced by the demands of flight. In the interest of weight reduction, some avian bones have been fused or reduced in size, and many of the bones in a bird's body are hollow and filled with air (pneumatized).

Birds have lightweight beaks instead of jaws filled with heavy teeth, and some internal organs are reduced in size or absent. Stability in flight is increased by the bird's overall body plan, which places its greatest mass in the centralized area between the wings, providing a compact center of gravity. To provide the power for flight, birds have exceptionally efficient circulatory and respiratory systems, the latter including a system of air sacs that assist with thermoregulation and buoyancy as well as offering some protection to internal organs. Control and rapid adjustments during flight are aided by the bird's sophisticated central nervous system and exceptional visual acuity.

The Evolution of Birds

There are two primary theories about bird origins. One theory suggests that birds arose from early (nondinosaur) reptiles, possibly those called thecodonts. The other proposes that birds evolved from a common ancestor with theropod dinosaurs. If the latter idea is true, then modern birds are "living dinosaurs."

Proponents of the thecodont theory point out that there are skeletal similarities between birds and thecodonts, most notably the presence of clavicles , which dinosaurs were thought to lack. However, fossil finds and reexamination of previously collected dinosaur fossils show that many groups of dinosaurs did, indeed, have clavicles. Proponents of the dinosaur theory point out that Archaeopteryx, the earliest fossil to be conclusively identified as having a close affinity to birds, has many anatomical features in common with theropod dinosaurs.

However, one argument against the dinosaur origin of birds has to do with the digits. In the avian wing, the bones of the "hand" include only three fingers. The "hand" of a theropod dinosaur also has only three fingers, but many paleontologists think that they are a different three than those that birds have retained.

Birds and the Environment

Birds range in size from the Cuban bee hummingbird, which is approximately 5.7 centimeters (2.25 inches) from bill tip to tail tip and weighs less than 31 grams (about 1 ounce), to the ostrich, which may stand 2.7 meters
(9 feet) tall and weigh over 136 kilograms (300 pounds). Birds are represented in the breeding fauna of all seven continents, and exploit habitats ranging from rainforests to deserts to oceans. The high mobility conferred by flight permits birds to colonize even the most remote areas. Some birds, however, particularly those residing on islands where there are few terrestrial predators, have secondarily evolved flightlessness.

Because birds are everywhere and highly visible, the health of bird populations can be valuable indicators of environmental health. Habitat destruction and/or fragmentation is probably the most important current threat to bird populations worldwide. Reducing a large area of contiguous habitat to several smaller parcels means that birds requiring large breeding territories will not be able to find them. Birds that can breed in the smaller parcels may also experience reduced breeding success because proximity of a nest to a habitat edge may increase the likelihood that it will be found by a predator or parasite .

Pesticides have also been implicated in reductions of bird populations. In particular, poisons may accumulate in the tissues of predatory birds at the top of the food chain, such as eagles, which consume many smaller predators that have been exposed to pesticides. An example is DDT, which results in the thinning of eggshells and consequent egg breakage during incubation. Some bird species have also been threatened by the introduction of non-native competitors and predators.

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bird

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

bird, warm-blooded, egg-laying, vertebrate animal having its body covered with feathers and its forelimbs modified into wings, which are used by most birds for flight. Birds compose the class Aves (see Chordata). There are an estimated 9,000 living species.

Birds are believed to be extant members of a group of dinosaurs called maniraptors (other maniraptors include Velociraptor and Oviraptor). They share with dinosaurs such characteristics as a foot with three primary toes and one accessory toe held high in back. Early birdlike animals include Arachaeopteryx, the ichthyornithiforms, skillful flyers with toothed beaks, Archaeornithura, and the rooster-sized, flightless Patagopteryx. The fossil remains of the Archaeopteryx, which date to the Jurassic period, show reptilian tails, jaws with teeth, and clawed wings, but feathers (found also in some dinosaurs) were well developed. Pterosaurs, another group of flying reptiles, did not share the common characteristics of birds and dinosaurs and are not considered birds. Whether the capacity for flight arose in tree-living dinosaurs that glided from branch to branch (the
"trees-down"
hypothesis) or in fast-running terrestrial dinosaurs (the
"ground-up"
hypothesis) continues to be debated. Indeed, the inclusion of birds in the dinosaur family tree, although accepted by most paleontologists, is debated by some, and the identification (2000) of feathers on a 220-million-year-old, four-legged reptile fossil, Longisquama insignis, raised questions concerning the theory. Archaeornithura, which dates to the Cretaceous period, is one of the earliest known ancestors of modern birds and resembles a modern wading bird.

Birds are of enormous value to humanity because of their destruction of insect pests and weed seeds. Many are useful as scavengers. The game birds hunted for food and sport include grouse, pheasant, quail, duck, and plover. The chief domestic birds are the chicken (see poultry), duck, goose, turkey, and guinea fowl. Parrots and many members of the finch family are kept as pets.

Characteristic Features and Behaviors

Like mammals, they have a four-chambered heart, and there is a complete separation of oxygenated and deoxygenated blood. The body temperature is from 2° to 14° higher than that of mammals. Birds have a relatively large brain, keen sight, and acute hearing, but little sense of smell. Birds are highly adapted for flight. Their structure combines lightness and strength. Body weight is reduced by the presence of a horny bill instead of heavy jaws and teeth and by the air sacs in the hollow bones as well as in other parts of the body. Compactness and firmness are achieved by the fusion of bones in the pelvic region and in other parts of the skeleton. The heavier parts of the body—the gizzard, intestines, flight muscles, and thigh muscles—are all strategically located for maintaining balance in flight. Feathers, despite their lightness, are highly protective against cold and wet. The flight feathers, especially, have great strength. Feathers are renewed in the process of molting. Some birds, such as the ostrich, the penguin, and the kiwi, lack the power of flight and have a flat sternum, or breastbone, without the prominent keel to which the well-developed flight muscles of other birds are attached. The bills of birds are well adapted to their food habits. Specialized bills are found in the crossbill, hummingbird, spoonbill, pelican, and woodpecker.

In the majority of species there are differences between male and female in plumage coloring. In these birds the male (except in the phalarope) is usually the more brilliant or the more distinctly marked and is the aggressor in courtship. Unusual courtship displays are performed by several species, particularly by the ruffed grouse, the bird of paradise, the crane, the pheasant, and the peacock. Birdsong reaches its highest development during the breeding season, and singing ability is usually either restricted to or superior in the male. Most birds build a nest in which to lay their eggs. Some birds, such as the oriole, weave an intricate structure, while others lay their eggs directly on the ground or among a few seemingly carelessly assembled twigs. Eggs vary in size, number, color, and shape. In spring and fall many birds migrate. Not all of the factors motivating this behavior are fully understood. These trips often involve flights of hundreds and even thousands of miles over mountains and oceans (see also migration of animals).

Bibliography

Among the periodicals devoted to the study of bird life are the Auk, the Condor, and the Wilson Bulletin. Books on birds include the many guides by R. T. Peterson; the life histories of North American birds in F. Gill and A. Poole, ed., The Birds of North America (1992–2003); R. M. De Schauensee, A Guide to the Birds of South America (1970); A. Rutgers and K. A. Norris, ed., Encyclopaedia of Aviculture (3 vol., 1970–77); U.S. Bureau of Sports Fisheries and Wildlife, Birds in Our Lives (1970); J. Van Tyne and A. J. Berger, Fundamentals of Ornithology (1971); S. Cramp, ed., Handbook of the Birds of Europe, the Middle East, and North Africa (5 vol., 1977–88); M. Walters, Birds of the World (1980); J. Farrand, Jr., Eastern Birds (1988) and Western Birds (1988); B. King et al., The Collins Field Guide to the Birds of South-East Asia (1988); S. Chatterjee, The Rise of Birds (1997); D. Attenborough, The Life of Birds (1998); P. Shipman, Taking Wing (1998); D. A. Sibley, The Sibley Guide to Birds (2000); T. Birkhead, The Wisdom of Birds: An Illustrated History of Ornithology (2009) and Bird Sense: What It's Like to Be a Bird (2012). A study of endangered birds and their habitats is Bird Watch (2011) by M. Walters.

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bird

bird used in a number of figurative and emblematic phrases.The bird has flown that the prisoner or fugitive has escaped; the expression was famously used by Charles I of his failed attempt to arrest the Five of Chancery in the House of Commons, 4 January 1642, when he found that the men had escaped.a bird in the hand is worth two in the bush it is better to accept what one has than to try to get more and risk losing everything. Recorded from the mid 15th century, but ‘one bird in the hands is worth more than two in the woods’ is found in 13th-century Latin. The saying was parodied by the American actress Mae West (1892–1980) in Belle of the Nineties (1934 film), ‘A man in the house is worth two in the street.’a bird never flew on one wing frequently used to justify a further gift, especially another drink; proverbial saying, recorded from the early 18th century, and found mainly in Scottish and Irish sources.Bird of Freedom the emblematic bald eagle of the US; the phrase is recorded from the mid 19th century.The bird of Jove is the eagle, which in classical mythology was sacred to Jove. The bird of Juno is the peacock, which in classical mythology was sacred to Juno.give someone the bird is to boo or jeer at someone. Earlier (early 19th century) in theatrical slang as the big bird, meaning a goose, because an audience's hissing an unpopular act or actor could be compared with the hissing of geese.

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bird

bird Any one of c.8600 species of feathered vertebrates, which occupy most natural habitats from deserts and tropics to polar wastes. Birds are warm-blooded and have forelimbs modified as wings, hind-limbs for walking, and jaws elongated into a toothless beak. They lay eggs (usually in nests), incubate the eggs, and care for young. As a group they feed on seeds, nectar, fruit and carrion, and hunt live prey ranging from insects to small mammals, although individual species may be very specialized in their diet. Sight is the dominant sense, smell the poorest. Size ranges from the bee hummingbird, 6.4cm (2.5in) to the wandering albatross, whose wingspread reaches 3.5m (11.5ft). The 2.4m (8ft) tall ostrich is the largest of living birds, but several extinct flightless birds were even bigger. Of the 27 orders of birds, the perching birds (Passeriformes) include more species than all others combined. A bird's body is adapted primarily for flight, with all its parts modified accordingly. There are several species of large, flightless land birds, including the ostrich, rhea, emu, cassowary, kiwi, and penguin. Birds are descended from Theocodonts (reptiles), and the first fossil bird, archaeopteryx, dates from the late Jurassic period. Class Aves. See individual species

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birds

birds an emblem of St Francis of Chancery.The birds and the bees an informal term for basic facts about sex and reproduction as told to a child.birds in their little nests agree a nursery proverb, also used as a direction, stating that young children should not argue among themselves, recorded from the early 18th century. ( Dr Johnson, describing Pembroke College, Oxford, said, ‘Sir, we are a nest of singing birds.’)birds of a feather flock together people of the same (usually, unscrupulous) character associated together. Recorded from the mid 16th century, and often now used allusively in ‘birds of a feather’. The Apocrypha (Ecclesiasticus 27:9) has the related ‘The birds will resort unto their like, so will truth return unto them that practise in her.’little birds that can sing and won't sing must be made to sing those who refuse to obey or cooperate will be forced to do so; saying recorded from the late 17th century.there are no birds in last year's nest circumstances have changed, and former opportunities are no longer there; saying recorded from the early 17th century.

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bird

bird
/ bərd/
•
n.
1.
a warm-blooded egg-laying vertebrate distinguished by the possession of feathers, wings, and a beak and (typically) by being able to fly. • Class Aves. ∎
an animal of this type that is hunted for sport or used for food:
carve the bird at the dinner table. ∎
a clay pigeon.
∎ inf.
an aircraft, spacecraft, satellite, or guided missile:
the crews worked frantically to ready their birds for flight.2. inf.
a person of a specified kind or character:
I'm a pretty tough old bird.PHRASES:the birds and the bees
basic facts about sex and reproduction, as told to a child.flip (or give) someone the bird
stick one's middle finger up at someone as a sign of contempt or anger.
(strictly) for the birds inf.
not worth consideration; unimportant:
this piece of legislation is for the birds.have a bird inf.
be very shocked or agitated:
the press corps would have a bird if the president-to-be appointed his wife to a real job.kill two birds with one stonesee kill1 .

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birds

birds A class (Aves) of endothermic (see endotherm) vertebrates that are adapted for flight, bipedal walking or running, and, in some species, swimming on or below the surface of water; flightless species (ratites) are believed to have diverged from flying birds and subsequently to have lost their adaptations for flight. The bones are light and often tubular, sometimes strengthened by internal struts, the body is covered with feathers, the forelimbs are modified to form wings, and the jaws, which are usually long and slender, lack teeth and support a horny bill. Many of the bones contain extensions of the air sacs. Except in ratites, which lack it, a keel on the sternum provides attachment for powerful flight muscles. Birds are descended from archosaurian reptiles and retain a number of reptilian characteristics (e.g. the arrangement of the parts of the skull and the scaly covering of the legs and feet; feathers are also derived from scales). The skin is thin and lacks sweat glands. There are about 8700 species, with a worldwide distribution.

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Birds

Encyclopedia of Occultism and Parapsychology
COPYRIGHT 2001 The Gale Group Inc.

Birds

It was a common belief amongst primitive tribes that the souls of the dead were conveyed to the land of the hereafter by birds. Some West African peoples would bind a bird to the body of the deceased and then sacrifice it to carry the man's soul to the afterworld. The Bagos also offered up a bird on the corpse of a deceased person for the same reason. The South Sea Islanders used to bury their dead in coffins shaped like the bird that was to bear away the spirits, while the natives of Borneo represented Tempon Telon's Ship of the Dead as having the form of a bird. The Native American tribes of the Northwest had rattles shaped like ravens with a large face painted on the breast. The probable significance is that the raven was to carry the disembodied soul to the region of the sun.

The flight of birds was also studied as part of the methods of divination in ornithomancy.

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bird

bird (obs. or dial.) young bird OE., feathered animal (in this sense supersending fowl); maiden, girl XIII. OE. brid, of unkn. orig. In the sense ‘maiden’ there may have been blending with ME. burde young woman, lady.

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